Switch device

ABSTRACT

In a semiconductor switch, a resistance value between a current input terminal to which a current is input and a current output terminal from which a current is output decreases as a voltage of a control terminal based on a potential of the current output terminal increases. A booster circuit is disposed on a path extending from the current input terminal to the control terminal. The booster circuit boosts a voltage input from the current input terminal side and applies the boosted voltage to the control terminal. A switch is connected between the control terminal and the current output terminal of the semiconductor switch. The switch is switched off by power consumption. The power consumption stops and the switch switches on if the supply of power to the booster circuit stops.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of PCT/JP2020/030834 filedon Aug. 14, 2020, which claims priority of Japanese Patent ApplicationNo. JP 2019-151934 filed on Aug. 22, 2019, the contents of which areincorporated herein.

TECHNICAL FIELD

The present disclosure relates to a switch device.

BACKGROUND

JP 2009-10477A discloses a vehicle switch device that controls thesupply of power from a battery to a load. In this switch device, acurrent flows from the battery to the load via a semiconductor switch.The semiconductor switch is an N-channel field-effect transistor (FET).The drain and the source of the semiconductor switch are respectivelydisposed on the battery side and the load side. An internal circuitswitches the semiconductor switch on by raising the gate voltage of thesemiconductor switch, and switches the semiconductor switch off bydecreasing the gate voltage of the semiconductor switch.

In the switch device disclosed in JP 2009-10477A, a switch is disposedbetween the gate and the source of the semiconductor switch. The switchis also an N-channel FET. The drain and the source of the switch arerespectively disposed on the gate side and the source side of thesemiconductor switch. A first resistor is connected between the gate andthe source of the switch.

In the switch device disclosed in JP 2009-10477A, a current flows fromthe positive electrode of the battery, through the internal circuit anda second resistor in this order, and back to the negative electrode ofthe battery. Thus, power is supplied to the internal circuit. Whilepower is being supplied to the internal circuit in such a manner, acurrent flows to the second resistor rather than the first resistor. Inthis case, the gate voltage based on the source potential is 0 V in theswitch, and the switch is off.

If a disconnection occurs in a connection line connecting the secondresistor and the negative electrode of the battery, i.e., if anabnormality occurs in the supply of power to the internal circuit, acurrent flows through the internal circuit and the first resistor inthis order. In this case, a voltage drop occurs in the first resistor,and thus a voltage is applied between the source and the gate of theswitch. Here, the gate voltage based on the source potential is higherthan or equal to a threshold in the switch, and the switch switches on.If the switch switches on, the gate voltage based on the sourcepotential decreases to 0 V in the semiconductor switch, and thesemiconductor switch is forced to switch off.

While the operation of the internal circuit may become unstable if adisconnection occurs in the connection line connecting the secondresistor and the negative electrode of the battery, the semiconductorswitch is forced to switch off in such a case. Therefore, no currentflows via the semiconductor switch, and thus the semiconductor switch isprevented from entering an abnormal state.

In the switch device disclosed in JP 2009-10477A, the voltage betweenboth terminals of the first resistor, i.e., the voltage between the gateand the source of the switch, is dependent on the voltage between bothterminals of the battery, the resistance value of the internal circuit,etc. Furthermore, these values may change. Accordingly, even if adisconnection occurs in the connection line connecting the secondresistor and the negative electrode of the battery, the voltage betweenthe gate and the source of the switch may not become higher than orequal to the threshold. In such a case, the switch does not switch on,and the semiconductor switch does not switch off.

In view of this, the present disclosure aims to provide a switch devicein which a semiconductor switch reliably switches off if an abnormalityconcerning power supply occurs.

SUMMARY

A switch device according to one aspect of the present disclosureincludes: a semiconductor switch in which a resistance value between acurrent input terminal to which a current is input and a current outputterminal from which a current is output decreases as a voltage of acontrol terminal based on a potential of the current output terminalincreases; a booster circuit that is disposed on a path extending fromthe current input terminal to the control terminal, and that boosts avoltage input from the current input terminal side and applies theboosted voltage to the control terminal; and a switch that is switchedoff by power consumption and that switches on if the power consumptionstops, wherein the switch is connected between the control terminal andthe current output terminal, and the power consumption concerning theswitch stops if the supply of power to the booster circuit stops.

Advantageous Effects

According to the present disclosure, a semiconductor switch reliablyswitches off if an abnormality concerning power supply occurs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram of a power supply system in embodiment 1.

FIG. 2 is a timing chart for describing the operation of a switchdevice.

FIG. 3 is a circuit diagram of a first switching circuit.

FIG. 4 is a timing chart for describing the operation of the firstswitching circuit.

FIG. 5 is a circuit diagram of a second switching circuit.

FIG. 6 is a graph illustrating a current characteristic of a secondswitch.

FIG. 7 is a circuit diagram of the power supply system in embodiment 2.

FIG. 8 is a timing chart for describing the operation of the switchdevice.

FIG. 9 is a circuit diagram of a first switching circuit.

FIG. 10 is a circuit diagram of a second switching circuit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First, aspects of the present disclosure will be listed and described.The embodiments described below may at least be partially combined asappropriate.

A switch device according to one aspect of the present disclosureincludes: a semiconductor switch in which a resistance value between acurrent input terminal to which a current is input and a current outputterminal from which a current is output decreases as a voltage of acontrol terminal based on a potential of the current output terminalincreases; a booster circuit that is disposed on a path extending fromthe current input terminal to the control terminal, and that boosts avoltage input from the current input terminal side and applies theboosted voltage to the control terminal; and a switch that is switchedoff by power consumption and that switches on if the power consumptionstops, wherein the switch is connected between the control terminal andthe current output terminal, and the power consumption concerning theswitch stops if the supply of power to the booster circuit stops.

In the above-described aspect, the booster circuit boosts the voltage ofthe current input terminal of the semiconductor switch and applies theboosted voltage to the control terminal of the semiconductor switch.Thus, the semiconductor switch switches on. If an abnormality concerningthe supply of power to the booster circuit occurs, i.e., if the supplyof power to the booster circuit stops, the switch switches on. Thus, thevoltage of the control terminal based on the potential of the currentoutput terminal decreases to 0 V in the semiconductor switch, and thesemiconductor switch switches off.

Because the switch switches on when power consumption is stopped, theswitch is switched on independently of the voltage of the current inputterminal of the semiconductor switch, the resistance value of thebooster circuit, etc. Consequently, if an abnormality concerning thesupply of power to the booster circuit occurs, the switch reliablyswitches on, and the semiconductor switch reliably switches off.

The switch device according to one aspect of the present disclosurefurther includes a second switch that is connected between the currentinput terminal and the booster circuit and that switches off if thesupply of power to the booster circuit stops.

In the above-described aspect, if an abnormality occurs in the supply ofpower to the booster circuit, i.e., if the supply of power to thebooster circuit stops, the second switch switches off and thus nocurrent flows from the booster circuit to the control terminal side ofthe semiconductor switch. Consequently, the amount of power consumed issuppressed.

In the switch device according to one aspect of the present disclosure,in regard to the switch, a resistance value between a controlterminal-side first terminal and a current output terminal-side secondterminal increases as a voltage of a second control terminal based on apotential of the second terminal decreases, the switch device furtherincludes a resistor that is connected between the second terminal andthe second control terminal, a current flows from the second terminalside to the second control terminal side via the resistor while thesemiconductor switch is on, and the current flow via the resistor stopsif the supply of power to the booster circuit stops.

In the above-described aspect, a current flows from the second terminalof the switch to the second control terminal of the switch via theresistor while power is being supplied to the booster circuit. In thiscase, the voltage of the second control terminal based on the potentialof the second terminal in the switch is a negative voltage and low. Theresistance value between the first terminal and the second terminal inthe switch is large, and the switch is off. If the supply of power tothe booster circuit stops, the current flow via the resistor stops, andthus, the voltage of the second control terminal based on the potentialof the second terminal increases to 0 V in the switch, and the switchswitches on.

The switch device according to one aspect of the present disclosurefurther includes a Zener diode which is connected between the firstterminal and the second control terminal of the switch, a cathode and ananode of the Zener diode being respectively disposed on the firstterminal side and the second control terminal side, wherein the boostercircuit boosts the voltage input from the current input terminal side toa target voltage, and a breakdown voltage of the Zener diode is higherthan the target voltage.

In the above-described aspect, because the breakdown voltage of theZener diode is higher than the target voltage, no current flows via theZener diode while the booster circuit is performing voltage boosting.Consequently, the amount of power consumed is suppressed.

Specific examples of a power supply system according to embodiments ofthe present disclosure will be described in the following with referenceto the drawings. Note that the present invention is not limited to theseexamples, and is intended to include all modifications that areindicated by the claims and are within the meaning and scope ofequivalents of the claims.

Embodiment 1 Configuration of Power Supply System

FIG. 1 is a circuit diagram of a power supply system 1 in embodiment 1.The power supply system 1 is suitably installed in a vehicle, andincludes a battery 10, a switch device 11, a load 12, a GND conductor13, and a connection terminal T1. The switch device 11 includes asemiconductor switch 20 and a connection terminal T2. The semiconductorswitch 20 is an N-channel FET.

The positive electrode of the battery 10 is connected to a drain 20 d ofthe semiconductor switch 20. A source 20 s of the semiconductor switch20 is connected to one terminal of the load 12. The negative electrodeof the battery 10 and the other terminal of the load 12 are connected tothe GND conductor 13. The connection terminal T1 is connected to the GNDconductor 13 via a connection line K1. For example, the GND conductor 13is the body of the vehicle. The connection to the GND conductor 13 isequivalent to grounding. The connection terminal T1 is detachablyconnected to the connection terminal T2 of the switch device 11.

The battery 10 supplies power to the load 12 via the semiconductorswitch 20 of the switch device 11. Here, a current flows from thepositive electrode of the battery 10, through the semiconductor switch20, the load 12, and the GND conductor 13 in this order, and back to thenegative electrode of the battery 10. In the semiconductor switch 20,the current is input to the drain 20 d and is output from the source 20s to the load 12. The drain 20 d and the source 20 s of thesemiconductor switch 20 respectively function as a current inputterminal and a current output terminal.

The load 12 is an electric device that is installed in the vehicle. Theload 12 operates while power is supplied thereto. The load 12 stopsoperating if the supply of power thereto stops.

If the connection terminal T1 is connected to the connection terminal T2of the switch device 11, a current flows from the positive electrode ofthe battery 10, through the switch device 11, the connection terminalT1, and the GND conductor 13 in this order, and back to the negativeelectrode of the battery 10. Thus, power is supplied to the switchdevice 11.

If power is supplied thereto, the switch device 11 controls the supplyof power from the battery 10 to the load 12 by switching thesemiconductor switch 20 on or off. If the switch device 11 switches thesemiconductor switch 20 on, power is supplied to the load 12, and theload 12 operates. If the switch device 11 switches the semiconductorswitch 20 off, the supply of power to the load 12 stops, and the load 12stops operating.

If the connection terminals T1 and T2 are disconnected from one anotheror a disconnection occurs in the connection line K1, the supply of powerfrom the battery 10 to the switch device 11 stops. If the supply ofpower from the battery 10 to the switch device 11 stops in such amanner, the switch device 11 switches the semiconductor switch 20 off.Thus, the supply of power from the battery 10 to the load 12 stops.

Configuration of Switch Device 11

In addition to the semiconductor switch 20 and the connection terminalT2, the switch device 11 includes a first switch 21, a second switch 22,a booster circuit 23, a control switch 24, a first switching circuit 25,a second switching circuit 26, a control circuit 27, capacitors C1, Cd,and Cs, diodes D1 and Dp, resistors R1, R2, and R3, and a Zener diodeZ1.

The first switch 21 is a P-channel FET. The second switch 22 is anN-channel FET. The second switch 22 is a junction FET. The capacitor Cdis connected between the drain 20 d and a gate 20 g of the semiconductorswitch 20. The capacitor Cs is connected between the source 20 s and thegate 20 g of the semiconductor switch 20. The capacitors Cd and Cs areparasitic capacitances that are formed in the manufacturing process ofthe semiconductor switch 20. The cathode and the anode of the diode Dpare respectively connected to the drain 20 d and the source 20 s of thesemiconductor switch 20. The diode Dp is a parasitic diode formed in themanufacturing process of the semiconductor switch 20.

The drain 20 d of the semiconductor switch 20 is connected to thebooster circuit 23, the first switching circuit 25, and the anode of thediode D1. The cathode of the diode D1 is connected to one terminal ofthe resistor R1. The other terminal of the resistor R1 is connected tothe source of the first switch 21 and one terminal of the capacitor C1.The other terminal of the capacitor C1 is connected to the connectionterminal T2. The source and the gate of the first switch 21 areconnected to the first switching circuit 25. The first switching circuit25 is also connected to the connection terminal T2. The drain of thefirst switch 21 is connected to the booster circuit 23.

Accordingly, the first switch 21 is connected between the drain 20 d ofthe semiconductor switch 20 and the booster circuit 23. The first switch21 functions as a second switch.

The booster circuit 23 is also connected to one terminal of the resistorR2 and the connection terminal T2. The other terminal of the resistor R2is connected to the gate 20 g of the semiconductor switch 20. The gate20 g of the semiconductor switch 20 is also connected to one terminal ofthe control switch 24, one terminal of the resistor R3, and the cathodeof the Zener diode Z1.

The other terminal of the control switch 24 and the anode of the Zenerdiode Z1 are connected to the source 20 s of the semiconductor switch20. The other terminal of the resistor R3 is connected to a drain 22 dof the second switch 22. A source 22 s of the second switch 22 isconnected to the source 20 s of the semiconductor switch 20. The drain22 d, a gate 22 g, and the source 22 s of the second switch 22 are eachseparately connected to the second switching circuit 26. The secondswitching circuit 26 is also connected to the connection terminal T2.

Accordingly, the second switch 22 is connected between the gate 20 g andthe source 20 s of the semiconductor switch 20.

The battery 10 charges the capacitor C1 via the diode D1 and theresistor R1. Here, a current flows from the positive electrode of thebattery 10, through the diode D1, the resistor R1, the capacitor C1, theconnection terminals T2 and T1, and the GND conductor 13 in this order,and back to the negative electrode of the battery 10. Power is stored inthe capacitor C1.

If the gate voltage based on the source potential is lower than a firstthreshold in the first switch 21, the first switch 21 is on, and acurrent can flow therethrough via the drain and the source of the firstswitch 21. If the gate voltage based on the source potential is higherthan or equal to the first threshold in the first switch 21, the firstswitch 21 is off, and no current flows therethrough via the drain andthe source of the first switch 21. The first threshold is a fixed valueand is set in advance.

The mode of the first switch 21 is an enhancement mode. Thus, the firstthreshold is a negative value. If the gate voltage based on the sourcepotential is 0 V in the first switch 21, the first switch 21 is off.

The first switching circuit 25 keeps the first switch 21 on under normalconditions. If the connection terminals T1 and T2 are disconnected fromone another or a disconnection occurs in the connection line K1, thefirst switching circuit 25 switches the first switch 21 off.

If the first switch 21 is on, the voltage between both terminals of thecapacitor C1 is input to the booster circuit 23. In the following, thevoltage between both terminals of the battery 10 is referred to as a“battery voltage”. The capacitor C1 smooths the voltage of the drain 20d of the semiconductor switch 20 based on the potential of the GNDconductor 13, i.e., the battery voltage, and outputs the smoothedvoltage to the booster circuit 23 via the first switch 21. Accordingly,even if the battery voltage fluctuates, the voltage input to the boostercircuit 23 is stable.

The battery 10 supplies power to the booster circuit 23. Here, a currentflows from the positive electrode of the battery 10, through the boostercircuit 23, the connection terminals T2 and T1, and the GND conductor 13in this order, and back to the negative electrode of the battery 10.When power is being supplied to the booster circuit 23, the first switch21 is on, and the booster circuit 23 boosts the voltage between bothterminals of the capacitor C1 input from the drain 20 d side of thesemiconductor switch 20 to a target voltage. The target voltage is afixed value and is set in advance. The target voltage is higher than themaximum value of the battery voltage.

If the connection terminals T1 and T2 are disconnected from one anotheror a disconnection occurs in the connection line K1, the supply of powerfrom the battery 10 to the booster circuit 23 stops. If the supply ofpower to the booster circuit 23 stops, the booster circuit 23 stopsoperating and does not perform voltage boosting. As discussed above, ifthe connection terminals T1 and T2 are disconnected from one another ora disconnection occurs in the connection line K1, the first switch 21switches off. Accordingly, if the supply of power to the booster circuit23 stops, the first switch 21 switches off.

The booster circuit 23 applies the boosted voltage, i.e., the targetvoltage, to the gate 20 g of the semiconductor switch 20 via theresistor R2. While the battery 10 is supplying power to the boostercircuit 23, the booster circuit 23 continues to apply the target voltageto the gate 20 g of the semiconductor switch 20. The target voltage is avoltage based on the potential of the GND conductor 13.

If the booster circuit 23 is performing voltage boosting, at least oneof the capacitors Cd and Cs is charged when the control switch 24 isoff. Here, a current flows from the positive electrode of the battery10, i.e., the drain 20 d of the semiconductor switch 20, and through thediode D1, the resistor R1, the first switch 21, the booster circuit 23,the resistor R2, and the gate 20 g of the semiconductor switch 20 inthis order. Accordingly, the first switch 21 and the booster circuit 23are disposed on the path of a current that flows from the drain 20 d ofthe semiconductor switch 20 to the gate 20 g of the semiconductor switch20.

If at least one of the capacitors Cd and Cs is charged, the voltage ofthe gate 20 g based on the potential of the source 20 s increases in thesemiconductor switch 20. When the control switch 24 is on, a closedcircuit is formed by the capacitor Cd, the control switch 24, and thediode Dp, and a closed circuit is formed by the capacitor Cs and thecontrol switch 24. Thus, the capacitors Cd and Cs discharge via thecontrol switch 24. If the power stored in the capacitor Cs equals 0 W,the voltage of the gate 20 g based on the potential of the source 20 sdecreases to 0 V in the semiconductor switch 20.

If the booster circuit 23 is performing voltage boosting, the voltagesof the gate 20 g, the source 20 s, and the drain 20 d of thesemiconductor switch 20 based on the potential of the GND conductor 13are substantially the same when the control switch 24 is on. Thus, ifthe control switch 24 is on, the capacitors Cd and Cs are not charged bythe target voltage output by the booster circuit 23. Here, the voltagedrop caused by the diode Dp is ignored.

In regard to the semiconductor switch 20, the resistance value betweenthe drain 20 d and the source 20 s decreases as the voltage of the gate20 g based on the potential of the source 20 s increases. The gate 20 gof the semiconductor switch 20 functions as a control terminal. When thecontrol switch 24 switches from on to off in a case in which the boostercircuit 23 is performing voltage boosting, the voltage of the gate 20 gbased on the potential of the source 20 s increases to a sufficientlyhigh voltage in the semiconductor switch 20, and the resistance valuebetween the drain 20 d and the source 20 s of the semiconductor switch20 decreases to a sufficiently small value. Consequently, thesemiconductor switch 20 switches on.

If the control switch 24 switches from off to on, the voltage of thegate 20 g based on the potential of the source 20 s decreases to 0 Vinthe semiconductor switch 20 as discussed above, and the resistance valuebetween the drain 20 d and the source 20 s of the semiconductor switch20 increases to a sufficiently large value. Consequently, thesemiconductor switch 20 switches off. The mode of the semiconductorswitch 20 is the enhancement mode. Accordingly, if the voltage of thegate 20 g based on the potential of the source 20 s is 0 V in thesemiconductor switch 20, the resistance value between the drain 20 d andthe source 20 s of the semiconductor switch 20 is sufficiently large,and the semiconductor switch 20 is off.

When the semiconductor switch 20 is off and the control switch 24 is on,the booster circuit 23 applies a voltage to the load 12 via the resistorR2. However, because the resistance value of the resistor R2 issufficiently larger than the resistance value of the load 12, thevoltage applied to the load 12 is sufficiently low. Consequently, theload 12 does not operate.

An operation signal for instructing the load 12 to operate and a stopsignal for instructing the load 12 to stop operating are input to thecontrol circuit 27. If the operation signal is input to the controlcircuit 27, the control circuit 27 switches the control switch 24 offand switches the semiconductor switch 20 on. Thus, power is supplied tothe load 12, and the load 12 operates. If the stop signal is input tothe control circuit 27, the control circuit 27 switches the controlswitch 24 on, and switches the semiconductor switch 20 off. Thus, thesupply of power to the load 12 stops, and the load 12 stops operating.

The Zener diode Z1 limits the voltage between the gate 20 g and thesource 20 s of the semiconductor switch 20 so as to be lower than orequal to a first breakdown voltage. The first breakdown voltage is afixed value, and is higher than the target voltage. If the voltage ofthe gate 20 g based on the potential of the source 20 s reaches thefirst breakdown voltage in the semiconductor switch 20, a current flowsthrough the cathode and the anode in this order in the Zener diode Z1.Thus, the voltage of the gate 20 g based on the potential of the source20 s does not exceed the first breakdown voltage in the semiconductorswitch 20. If the voltage of the gate 20 g based on the potential of thesource 20 s is lower than the first breakdown voltage in thesemiconductor switch 20, no current flows via the Zener diode Z1.

If the voltage of the gate 22 g based on the potential of the source 22s is higher than or equal to a second threshold in the second switch 22,the second switch 22 is on, and a current can flow therethrough via thedrain 22 d and the source 22 s of the second switch 22. If the voltageof the gate 22 g based on the potential of the source 22 s is lower thanthe second threshold in the second switch 22, the second switch 22 isoff, and no current flows therethrough via the drain 22 d and the source22 s of the second switch 22. The second threshold is a fixed value andis set in advance.

The mode of the second switch 22 is a depletion mode. Thus, the secondthreshold is a negative value. If the voltage of the gate 22 g based onthe potential of the source 22 s is 0 V in the second switch 22, thesecond switch 22 is on.

If the semiconductor switch 20 switches on, the second switching circuit26 switches the second switch 22 off. If the semiconductor switch 20switches off, the second switching circuit 26 switches the second switch22 on. Here, the booster circuit 23 applies a voltage to the load 12 viathe resistors R2 and R3, and the second switch 22. However, because thecombined resistance value of the resistors R2 and R3 is sufficientlylarger than the resistance value of the load 12, the voltage applied tothe load 12 is sufficiently low. Consequently, the load 12 does notoperate.

If the connection terminals T1 and T2 are disconnected from one anotheror a disconnection occurs in the connection line K1, the secondswitching circuit 26 switches the second switch 22 on.

Suppose that the control switch 24 is off in a case in which the boostercircuit 23 is performing voltage boosting. In this case, as discussedabove, the capacitors Cd and Cs are charged, and the semiconductorswitch 20 is on. If the connection terminals T1 and T2 are disconnectedfrom one another or a disconnection occurs in the connection line K1 inthis state, the second switching circuit 26 switches the second switch22 on.

When the second switch 22 is on, a closed circuit is formed by thecapacitor Cd, the resistor R3, the second switch 22, and the diode Dp,and a closed circuit is formed by the capacitor Cs, the resistor R3, andthe second switch 22. Thus, the capacitors Cd and Cs discharge via thecontrol switch 24. Accordingly, the voltage of the gate 20 g based onthe potential of the source 20 s decreases to 0 V in the semiconductorswitch 20, and the semiconductor switch 20 switches off.

FIG. 2 is a timing chart for describing the operation of the switchdevice 11. In FIG. 2, the operation of the booster circuit 23, and thestates of the first switch 21, the second switch 22, the control switch24, and the semiconductor switch 20 are illustrated.

As discussed above, while power is being supplied to the booster circuit23, the first switching circuit 25 keeps the first switch 21 on, and thebooster circuit 23 continues to boost the voltage between both terminalsof the capacitor C1 to the target voltage. If the control circuit 27switches the control switch 24 off in this state, the semiconductorswitch 20 switches on. If the control circuit 27 switches the controlswitch 24 on, the semiconductor switch 20 switches off.

If the semiconductor switch 20 switches off, the second switchingcircuit 26 switches the second switch 22 on. If the semiconductor switch20 switches on, the second switching circuit 26 switches the secondswitch 22 off.

If the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1, the booster circuit23 stops performing voltage boosting. Furthermore, the first switchingcircuit 25 switches the first switch 21 off and the second switchingcircuit 26 switches the second switch 22 on, irrespective of the stateof the control switch 24.

If the first switch 21 is off, no current flows via the booster circuit23, which has stopped operating, and the resistor R2. Furthermore, whenthe second switch 22 is on, the capacitors Cd and Cs discharge, and thesemiconductor switch 20 switches off as discussed above.

Thus, if the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1, the semiconductorswitch 20 switches off.

An example of a conventional configuration for switching thesemiconductor switch 20 off in a case in which the connection terminalsT1 and T2 are disconnected from one another or a disconnection occurs inthe connection line K1 is a configuration in which the other terminal ofthe resistor R3 is directly connected to the source 20 s of thesemiconductor switch 20. In this case as well, the capacitors Cd and Cswould discharge via the resistor R3, and the semiconductor switch 20would switch off when the connection terminals T1 and T2 aredisconnected from one another or a disconnection occurs in theconnection line K1. However, in this configuration, a current wouldcontinue to flow from the booster circuit 23 through the resistors R2and R3 in this order while the booster circuit 23 is performing voltageboosting, and thus a large amount of power would be consumed.

As a result of disposing the second switch 22 in the switch device 11,no current flows from the booster circuit 23 to the load 12 unless thevoltage between the gate 20 g and the source 20 s of the semiconductorswitch 20 reaches a first breakdown voltage. Thus, a small amount ofpower is consumed.

In the following, the configurations of the first switching circuit 25and the second switching circuit 26 will be described one by one.

Configuration of First Switching Circuit

FIG. 3 is a circuit diagram of the first switching circuit 25. The firstswitching circuit 25 includes a circuit switch 30, a regulator 31, andresistors RA, R5, R6, and R7. The circuit switch 30 is an N-channel FET.The resistor RA is connected between the source and the gate of thefirst switch 21. One terminal of the resistor R5 is connected to thegate of the first switch 21. The other terminal of the resistor R5 isconnected to the drain of the circuit switch 30. The source of thecircuit switch 30 is connected to the connection terminal T2.

The resistor R6 is connected between the gate and the source of thecircuit switch 30. One terminal of the resistor R7 is also connected tothe gate of the circuit switch 30. The other terminal of the resistor R7is connected to the regulator 31. The regulator 31 is also connected tothe drain 20 d of the semiconductor switch 20, i.e., the positiveelectrode of the battery 10, and is connected to the connection terminalT2.

If the gate voltage based on the source potential is higher than orequal to a third threshold in the circuit switch 30, the circuit switch30 is on. If the gate voltage based on the source potential is lowerthan the third threshold in the circuit switch 30, the circuit switch 30is off. The third threshold is a fixed value and is set in advance. Themode of the circuit switch 30 is the enhancement mode. Thus, the thirdthreshold is a positive value. If the gate voltage based on the sourcepotential is 0 V, the circuit switch 30 is off.

The battery 10 supplies power to the regulator 31. Here, a current flowsfrom the positive electrode of the battery 10, through the regulator 31,the connection terminals T2 and T1, and the GND conductor 13 in thisorder, and back to the negative electrode of the battery 10. If power issupplied to the regulator 31, the regulator 31 steps down the voltage ofthe drain 20 d of the semiconductor switch 20 based on the potential ofthe GND conductor 13, i.e., the battery voltage, to a fixed set voltagethat is set in advance, and outputs the stepped-down voltage to theresistor R7. Thus, a voltage is applied between the gate and the sourceof the circuit switch 30 because a current flows through the resistorsR7 and R6 in this order, and a voltage drop occurs in the resistor R6.

Consequently, the gate voltage based on the source potential becomeshigher than or equal to the third threshold in the circuit switch 30,and the circuit switch 30 switches on. The circuit switch 30 is kept onwhile power is being supplied to the regulator 31.

As discussed above, if the gate voltage based on the source potential islower than the first threshold in the first switch 21, the first switch21 is on. If the gate voltage based on the source potential is higherthan or equal to the first threshold in the first switch 21, the firstswitch 21 is off. The first threshold is a negative value.

When the circuit switch 30 is on, a current flows from the positiveelectrode of the battery 10 and through the diode D1, and the resistorsR1, R4, and R5 in this order, or flows from one terminal of thecapacitor C1 and through the resistors R4 and R5 in this order. Thus, avoltage drop occurs in the resistor R4, and a voltage is applied betweenthe gate and the source of the first switch 21. Consequently, the gatevoltage based on the source potential is lower than the first thresholdin the first switch 21, and the first switch 21 is off. In such amanner, if the circuit switch 30 is on, the first switch 21 is on.

If the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1, the battery 10 stopssupplying power to the regulator 31. In this case, the regulator 31stops outputting a voltage to the resistor R7. If the regulator 31 stopsoutputting the voltage, no current flows through the resistors R7 andR6, and thus the voltage between the gate and the source of the circuitswitch 30 decreases to 0 V, and the circuit switch 30 switches off. 0 Vis lower than the third threshold.

If the circuit switch 30 switches off, the current flow via theresistors RA and R5 stops, and thus the gate voltage based on the sourcepotential increases to 0 V in the first switch 21, and the first switchswitches off. 0 V is higher than or equal to the first threshold.

FIG. 4 is a timing chart for describing the operation of the firstswitching circuit 25. The states of the circuit switch 30 and the firstswitch 21 are illustrated in FIG. 4. If power is supplied to the boostercircuit 23, the battery 10 also supplies power to the regulator 31, andthe regulator 31 outputs a voltage to the resistor R7. Thus, the circuitswitch 30 is on. As discussed above, if the circuit switch 30 is on, thefirst switch 21 is on.

If the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1 connecting theconnection terminal T1 and the GND conductor 13, the supply of power tothe regulator 31 also stops, and the regulator 31 stops outputting avoltage. Thus, the circuit switch 30 switches off. As discussed above,if the circuit switch 30 switches off, the first switch 21 switches off.

In such a manner, the first switching circuit 25 switches the firstswitch 21 from on to off if the supply of power to the booster circuit23 stops.

Note that it suffices for the circuit switch 30 to be a switch thatswitches on if the voltage of a control terminal based on the potentialof an output terminal from which a current is output becomes higher thanor equal to the third threshold, and switches off if the voltage of thecontrol terminal based on the potential of the output terminal fallsbelow the third threshold. Thus, the circuit switch 30 is not limited toan N-channel FET, and may be an NPN bipolar transistor, for example. Inthis case, the drain, the source, and the gate of the FET respectivelycorrespond to the collector, the emitter, and the base of the bipolartransistor.

Configuration of Second Switching Circuit

FIG. 5 is a circuit diagram of the second switching circuit 26. Thesecond switching circuit 26 includes resistors R8 and R9, and a Zenerdiode Z2. The resistor R8 is connected between the source 22 s and thegate 22 g of the second switch 22. The gate 22 g of the second switch 22is connected to one terminal of the resistor R9. The other terminal ofthe resistor R9 is connected to the connection terminal T2. The Zenerdiode Z2 is connected between the drain 22 d and the gate 22 g of thesecond switch 22. The cathode and the anode of the Zener diode Z2 arerespectively disposed on the drain 22 d-side and the gate 22 g-side ofthe second switch 22.

As discussed above, if the voltage of the gate 22 g based on thepotential of the source 22 s is higher than or equal to the secondthreshold in the second switch 22, the second switch 22 is on. If thevoltage of the gate 22 g based on the potential of the source 22 s islower than the second threshold in the second switch 22, the secondswitch 22 is off. The second threshold is a negative value.

FIG. 6 is a graph illustrating a current characteristic of the secondswitch 22. Vgs indicates the voltage of the gate 22 g based on thepotential of the source 22 s in the second switch 22. Ids indicates thecurrent that can flow via the drain 22 d and the source 22 s in thesecond switch 22. The greater the current Ids is, the smaller theresistance value between the drain 22 d and the source 22 s of thesecond switch 22 is. As illustrated in FIG. 6, as the voltage Vgsdecreases, the current Ids decreases, and the resistance value betweenthe drain 22 d and the source 22 s of the second switch 22 increases.The drain 22 d, the source 22 s, and the gate 22 g of the second switch22 respectively function as a first terminal, a second terminal, and asecond control terminal.

While the semiconductor switch 20 is on in a state in which theconnection terminals T1 and T2 are connected to one another and theconnection terminal T1 is connected to the GND conductor 13 via theconnection line K1, a current flows from the positive electrode of thebattery 10, through the semiconductor switch 20, the resistors R8 andR9, the connection terminals T2 and T1, and the GND conductor 13 in thisorder, and back to the negative electrode of the battery 10, asillustrated in FIG. 5. Thus, power is consumed by the resistor R8, avoltage drop occurs in the resistor R8, and a voltage is applied betweenthe source 22 s and the gate 22 g of the second switch 22. Here, thevoltage Vgs is lower than the second threshold, and thus the secondswitch 22 is off.

If the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1, the current flow viathe resistors R8 and R9 stops, and the consumption of power by theresistor R8 stops. If the power consumption stops, the voltage ceases tofall in the resistor R8, and thus the voltage Vgs increases to 0 V, andthe second switch 22 switches on.

As discussed above, if the control circuit 27 switches the controlswitch 24 from off to on, the semiconductor switch 20 switches off. Ifthe semiconductor switch 20 switches off, the current flow via theresistors R8 and R9 also stops, and thus the second switch 22 switcheson. If the control circuit 27 switches the control switch 24 from on tooff, the semiconductor switch 20 switches on, power is consumed by theresistor R8, and the second switch 22 switches off.

If the connection terminals T1 and T2 are disconnected from one anotheror a disconnection occurs in the connection line K1, an abnormalityconcerning the supply of power to the booster circuit 23 occurs, and thesupply of power to the booster circuit 23 stops. Here, the second switch22 switches on. Thus, the voltage of the gate 20 g based on thepotential of the source 20 s decreases to 0 V in the semiconductorswitch 20, and the semiconductor switch 20 switches off.

As discussed above, if a current flows through the resistors R8 and R9and power is consumed, the second switch 22 switches off. If the currentflow via the resistors R8 and R9 stops and the power consumption stops,the second switch 22 switches on. Thus, the second switch 22 switches onindependently of the battery voltage, the resistance value of thebooster circuit 23, etc. Consequently, if an abnormality concerning thesupply of power to the booster circuit 23 occurs, the second switch 22reliably switches on, and the semiconductor switch 20 reliably switchesoff.

Furthermore, if an abnormality in the supply of power to the boostercircuit 23 occurs, no current flows from the drain 20 d of thesemiconductor switch 20 and via the booster circuit 23 and the secondswitch 22 because the first switch 21 switches off. Consequently, theamount of power consumed is suppressed.

The Zener diode Z2 limits the voltage between the drain 22 d and thegate 22 g of the second switch 22 so as to be lower than or equal to asecond breakdown voltage. The second breakdown voltage is a fixed value,and is higher than the target voltage output by the booster circuit 23.If the voltage of the drain 22 d based on the potential of the gate 22 greaches the second breakdown voltage in the second switch 22, a currentflows through the cathode and the anode in this order in the Zener diodeZ2. Thus, the voltage between the gate 22 g and the drain 22 d of thesecond switch 22 does not exceed the second breakdown voltage. If thevoltage of the drain 22 d based on the potential of the gate 22 g islower than the second breakdown voltage in the second switch 22, nocurrent flows via the Zener diode Z2.

Because the second breakdown voltage is higher than the target voltageas discussed above, no current flows via the Zener diode Z2 while thebooster circuit 23 is performing voltage boosting. Consequently, theamount of power consumed is further suppressed.

Note that it suffices for the first switch 21 to be a switch thatswitches on if the voltage of a control terminal based on the potentialof one terminal on the resistor R1-side falls below the first threshold,and switches off if the voltage of the control terminal based on thepotential of the one terminal on the resistor R1-side becomes higherthan or equal to the first threshold. Thus, the first switch 21 is notlimited to a P-channel FET, and may be a PNP bipolar transistor, forexample.

Furthermore, it suffices for the second switch 22 to have twocharacteristics. The first characteristic is a characteristic that theresistance value thereof increases as the voltage of a control terminalbased on the potential of one terminal on the source 20 s side of thesemiconductor switch 20 decreases. The second characteristic is acharacteristic that the second switch 22 is on when the voltage of thecontrol terminal based on the potential of the one terminal on the sideof the source 20 s of the semiconductor switch 20 is 0 V. Thus, thesecond switch 22 is not limited to a junction FET. Accordingly, if thesecond switch 22 is a depletion mode N-channel FET, the second switch 22does not have to be a junction FET.

Embodiment 2

In embodiment 1, switches that are realized by semiconductors are usedas the first switch 21 and the second switch 22. The switch for stoppingthe input of a current from the resistor R1 to the booster circuit 23and the switch connected between the gate 20 g and the source 20 s ofthe semiconductor switch 20 are not limited to switches realized bysemiconductors.

In the following, the differences of embodiment 2 from embodiment 1 willbe described. Because configurations in embodiment 2 other than thosedescribed in the following are the same as those in embodiment 1, thesame reference symbols as those given in embodiment 1 are given tocomponents that are the same as those in embodiment 1, and descriptionthereof will be omitted.

Configuration of Switch Device

FIG. 7 is a circuit diagram of the power supply system 1 in embodiment2. When embodiment 2 is compared with embodiment 1, the switch device 11has a different configuration. The switch device 11 in embodiment 2includes, among the components of the switch device 11 in embodiment 1,the components other than the first switch 21, the second switch 22, thefirst switching circuit 25, the second switching circuit 26, and theresistor R3, and such components are connected in a similar manner as inembodiment 1.

The switch device 11 in embodiment 2 includes a first switch 21 a, asecond switch 22 a, a first switching circuit 25 a, and a secondswitching circuit 26 a in place of the first switch 21, the secondswitch 22, the first switching circuit 25, and the second switchingcircuit 26. The first switch 21 a and the second switch 22 a are relaycontacts.

The first switch 21 a is connected between the booster circuit 23 and aconnection node between the resistor R1 and the capacitor C1. The secondswitch 22 a is connected between the gate 20 g and the source 20 s ofthe semiconductor switch 20.

Operation of Switch Device

FIG. 8 is a timing chart for describing the operation of the switchdevice 11. In FIG. 8, the operation of the booster circuit 23, and thestates of the first switch 21 a, the second switch 22 a, the controlswitch 24, and the semiconductor switch 20 are illustrated as in FIG. 2.The booster circuit 23, the control switch 24, and the semiconductorswitch 20 function in a similar manner.

The first switching circuit 25 a operates in a similar manner as thefirst switching circuit 25 in embodiment 1. Accordingly, the firstswitching circuit 25 a keeps the first switch 21 a on while the boostercircuit 23 is performing voltage boosting. If the supply of power to thebooster circuit 23 stops due to the connection terminals T1 and T2 beingdisconnected from one another or a disconnection occurring in theconnection line K1, the first switching circuit 25 a switches the firstswitch 21 a from on to off.

The second switching circuit 26 a keeps the second switch 22 a off whilethe booster circuit 23 is performing voltage boosting, irrespective ofthe state of the semiconductor switch 20. If the supply of power to thebooster circuit 23 stops due to the connection terminals T1 and T2 beingdisconnected from one another or a disconnection occurring in theconnection line K1, the second switching circuit 26 a switches thesecond switch 22 a from off to on. When the second switch 22 a switcheson in a case in which the semiconductor switch 20 is on, the voltage ofthe gate 20 g based on the potential of the source 20 s decreases to 0 Vin the semiconductor switch 20, and the semiconductor switch 20 switchesoff.

In such a manner, if the connection terminals T1 and T2 are disconnectedfrom one another or a disconnection occurs in the connection line K1, anabnormality concerning the supply of power to the booster circuit 23occurs, and the supply of power to the booster circuit 23 stops. Here,the second switch 22 a switches on, and the semiconductor switch 20switches off. Furthermore, if an abnormality in the supply of power tothe booster circuit 23 occurs, no current flows from the drain 20 d ofthe semiconductor switch 20 and via the booster circuit 23 and thesecond switch 22 a because the first switch 21 a switches off.Consequently, the amount of power consumed is suppressed.

Configuration of First Switching Circuit

FIG. 9 is a circuit diagram of the first switching circuit 25 a. Thefirst switching circuit 25 a includes a resistor R10 and an inductor L1.One terminal of the resistor R10 is connected to the drain 20 d of thesemiconductor switch 20, i.e., the positive electrode of the battery 10.The other terminal of the resistor R10 is connected to one terminal ofthe inductor L1. The other terminal of the inductor L1 is connected tothe connection terminal T2.

In the first switch 21 a, an end portion of a bar-shaped first conductoris pivotably connected to one terminal. If the first conductor is incontact with the other terminal, the first switch 21 a is on. If thefirst conductor is separated from the other terminal, the first switch21 a is off. In the first switch 21 a, the first conductor is pulledaway from the other terminal by a spring, for example.

If the connection terminals T1 and T2 are connected to one another andthe connection terminal T1 is connected to the GND conductor 13 via theconnection line K1, a current flows from the positive electrode of thebattery 10, through the resistor R10, the inductor L1, the connectionterminals T2 and T1, and the GND conductor 13 in this order, and back tothe negative electrode of the battery 10. While a current is flowingthrough the inductor L1, the inductor L1 functions as a magnet andattracts the first conductor of the first switch 21 a to the otherterminal side of the first switch 21 a so that the first conductor isbrought into contact with the other terminal in the first switch 21 a.Thus, if the connection terminals T1 and T2 are connected to one anotherand the connection terminal T1 is connected to the GND conductor 13 viathe connection line K1, the first switch 21 a is on.

If the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1, the current flow viathe inductor L1 stops. Thus, the inductor L1 stops functioning as amagnet. Consequently, the first conductor separates from the otherterminal in the first switch 21 a, and the first switch 21 a switchesoff.

Configuration of Second Switching Circuit

FIG. 10 is a circuit diagram of the second switching circuit 26 a. Thesecond switching circuit 26 a includes a resistor R11 and an inductorL2. One terminal of the resistor R11 is connected to the drain 20 d ofthe semiconductor switch 20, i.e., the positive electrode of the battery10. The other terminal of the resistor R11 is connected to one terminalof the inductor L2. The other terminal of the inductor L2 is connectedto the connection terminal T2.

In the second switch 22 a, an end portion of a bar-shaped secondconductor is pivotably connected to one terminal. If the secondconductor is in contact with the other terminal, the second switch 22 ais on. If the second conductor is separated from the other terminal, thesecond switch 22 a is off. In the second switch 22 a, the secondconductor is pulled by a spring, for example, so as to be kept incontact with the other terminal.

If the connection terminals T1 and T2 are connected to one another andthe connection terminal T1 is connected to the GND conductor 13 via theconnection line K1, a current flows from the positive electrode of thebattery 10, through the resistor R11, the inductor L2, the connectionterminals T2 and T1, and the GND conductor 13 in this order, and back tothe negative electrode of the battery 10. While a current is flowingthrough the inductor L2, the inductor L2 functions as a magnet andattracts the second conductor of the second switch 22 a in a directionaway from the other terminal of the second switch 22 a so that thesecond conductor is separated from the other terminal in the secondswitch 22 a. Thus, if the connection terminals T1 and T2 are connectedto one another and the connection terminal T1 is connected to the GNDconductor 13 via the connection line K1, the second switch 22 a is off.

If the supply of power to the booster circuit 23 stops due to theconnection terminals T1 and T2 being disconnected from one another or adisconnection occurring in the connection line K1, the current flow viathe inductor L2 stops. Thus, the inductor L2 stops functioning as amagnet. Consequently, the second conductor comes into contact with theother terminal once again in the second switch 22 a, and the secondswitch 22 a switches on.

In such a manner, the second switch 22 a switches off if a current flowsthrough the resistor R11 and the inductor L2 and power is consumed inthe second switching circuit 26 a. If the current flow via the resistorR11 and the inductor L2 stops and the power consumption stops, thesecond switch 22 a switches on. Thus, the second switch 22 a switches onindependently of the battery voltage, the resistance value of thebooster circuit 23, etc. Consequently, if an abnormality concerning thesupply of power to the booster circuit 23 occurs, the second switch 22 areliably switches on, and the semiconductor switch 20 reliably switchesoff.

Note that, in the switch device 11 in embodiment 1, the first switch 21a and the first switching circuit 25 a in embodiment 2 may be used inplace of the first switch 21 and the first switching circuit 25.Similarly, in the switch device 11 in embodiment 1, the second switch 22a and the second switching circuit 26 a in embodiment 2 may be used inplace of the second switch 22 and the second switching circuit 26.

In embodiments 1 and 2, it suffices for the semiconductor switch 20 tobe a switch in which the resistance value between a current inputterminal to which a current is input and a current output terminal fromwhich a current is output decreases as the voltage of a control terminalbased on the potential of the current output terminal increases. Thus,the semiconductor switch 20 is not limited to an N-channel FET, and maybe an insulated-gate bipolar transistor (IGBT), an NPN bipolartransistor, or the like.

Embodiments 1 and 2 disclosed herein are examples in every way, andshall be construed as being non-limiting. The scope of the presentinvention is not limited to what is defined above, and is intended toinclude all modifications that are indicated by the claims and arewithin the meaning and scope of equivalents of the claims.

1. A switch device comprising: a semiconductor switch in which aresistance value between a current input terminal to which a current isinput and a current output terminal from which a current is outputdecreases as a voltage of a control terminal based on a potential of thecurrent output terminal increases; a booster circuit that is disposed ona path extending from the current input terminal to the controlterminal, and that boosts a voltage input from the current inputterminal side and applies the boosted voltage to the control terminal;and a switch that is switched off by power consumption and that switcheson if the power consumption stops, wherein the switch is connectedbetween the control terminal and the current output terminal, and thepower consumption concerning the switch stops if the supply of power tothe booster circuit stops.
 2. The switch device according to claim 1further including a second switch that is connected between the currentinput terminal and the booster circuit and that switches off if thesupply of power to the booster circuit stops.
 3. The switch deviceaccording to claim 1, wherein, in regard to the switch, a resistancevalue between a control terminal-side first terminal and a currentoutput terminal-side second terminal increases as a voltage of a secondcontrol terminal based on a potential of the second terminal decreases,the switch device further comprises a resistor that is connected betweenthe second terminal and the second control terminal, a current flowsfrom the second terminal side to the second control terminal side viathe resistor while the semiconductor switch is on, and the current flowvia the resistor stops if the supply of power to the booster circuitstops.
 4. The switch device according to claim 3 further including aZener diode which is connected between the first terminal and the secondcontrol terminal of the switch, a cathode and an anode of the Zenerdiode being respectively disposed on the first terminal side and thesecond control terminal side, wherein the booster circuit boosts thevoltage input from the current input terminal side to a target voltage,and a breakdown voltage of the Zener diode is higher than the targetvoltage.
 5. The switch device according to claim 2, wherein, in regardto the switch, a resistance value between a control terminal-side firstterminal and a current output terminal-side second terminal increases asa voltage of a second control terminal based on a potential of thesecond terminal decreases, the switch device further comprises aresistor that is connected between the second terminal and the secondcontrol terminal, a current flows from the second terminal side to thesecond control terminal side via the resistor while the semiconductorswitch is on, and the current flow via the resistor stops if the supplyof power to the booster circuit stops.